Method of etching aluminum foil in the manufacturing of aluminum electrolytic condensers



NOV. 11, 1969 TAKEsH| NAM|KATA ET AL 3,477,929

METHOD OF ETCHING ALUMINUM FOIL IN THE MANUFACTURING 0F ALUMINUM ELECTROLYTIC CONDENSERS Filed April 14, 1967 2 Sheets-Sheet 1 FIG. I

zloo u so go l I l l l I I I l o 20 40 so I00 TEMPERATURE PULSATING RATIO NOV. 11, 1969 TAKE5H| NAMlKATA ETAL 3,477,929

METHOD OF ETCHING ALUMINUM FOIL IN THE MANUFACTURING OF ALUMINUM ELECTROLYTIC CONDENSERS Filed April 14, 1967 2 Sheets-Sheet 2 F l G 3 o I l l l l l I l l 0.2 0.4 0.6 0.8 L0 CURRENT DENSITY [A/cm 1 l 1 1 ll 1" 2O 4O '60 80 I00 I20 FORMATION OF VOLTAGE [V] MAGNIFICATION OF ETCHlNG United States Patent T 3 477 929 METHOD OF ETCHIN G A LUMINUM FOIL IN THE MANUFACTURING OF ALUMINUM ELECTRO- LYTIC CONDENSERS Takeshi Namikata and Kazuo Kubo, Kawasaki-ski, Japan, I

assignors to Fujitsu Limited, Kawasaki, Japan, a corporation of Japan Filed Apr. 14, 1967, Ser. No. 630,972

' Claims priority, application Japan, Apr. 18, 1966,

41/24,542 Int. Cl. C23b 3/02 US. Cl. 204-141 8 Claims ABSTRACT OF THE DISCLOSURE Method ofetching an aluminum electrode required in the manufacturing process of the electrolytic condenser by applying a pulsating direct current to the aluminum electrode immersed in an aqueous solution made up essentially of 01- of 0.020.2 mol/1. and Crop" of 0.02- 0.1 mol/l.

Our invention relates to a method of manufacturing aluminum electrolytic condensers. In the manufacture of an aluminum electrolytic condenser, the aluminum anode element is etched to increase the effective surface area of the aluminum anode element thus increasing the capacity of the condenser.

In the conventional method, the aluminum anode ele ment is etched electrolytically in a liquid including a large amount of halogen ion. For example, the aluminum anode element is etched electrolytically in an etchant comprising a 16% aqueous solution of HCl using a steady (nonpulsating) direct current at a temperature of about 70 C. for several minutes. However, since a relatively high halogen concentration is present, the entire surface can only be etched to a depth of less than 20s. It is, therefore, impossible to make the surface area broader than a certain value. Furthermore, since the etching liquid is a weak acid, the pH gradually increases as the etching proceeds and aluminum hydroxide precipitate (or settlings) is produced. These settlings lower the conductivity of the liquid and raise the bath voltage as they are precipitated on the electrode.

Our invention has as an object the obviating of the above-mentioned defects and increasing the effective surface area of the aluminum anode element and inhibiting the settlings of aluminum hydroxide. Our invention makes the aluminum anode element porous by etching. We add corrosion inhibitors, such as chromic acid and chromate, to a solution including halogen ion. The chromic acid simultaneously inhibits the settlings of aluminum hydroxide. We have also found that in the etching of the anode element to make it porous, the etching effectivity can be increased by properly selecting the wave form of the current used and the temperature 'of the liquid. A pulsating current with a pulsating ratio of voltage [(the maximum value of a voltage-the minimum value of voltage)/the average value of voltage] of 15-3 is well suited as the current wave form and 65-85 C. is the optimum temperature. Moreover, in order to further inhibit the settlings of aluminum hydroxide, we lower the pH by adding inorganic acids such as HNO H PO and H 80, in an amount that the etching form may not be affected.

In the drawings, FIGS. 1, 2, 3 and 4 respectively show variations of magnification (increase) of etching on the ordinate versus, respectively, temperature, pulsating ratio, current density and voltage.

Characteristic features of our etching method:

(1) The etching phenomenon cannot occur if the Clconcentration is too low, and the etching proceeds uniformly if the Clconcentration is too high. In order to etch the anode element to make it porous, the Clconcentration should be 0.02-0.2 mol/l. with 0.1. mol/l. the optimum value.

(2) If the cro,- concentration is too much lower than the Cl concentration, only the effect of Clappears. It thus becomes difficult to make the anode element porous. On the other hand, if the CrOp concentration is too high, the etching or eroding property of Cl'" is inhibited and a thick film is formed on the surface of the element by the protective property of CrO," thus preventing etching of the element. When the CrOg" concentration is 0.02- 0.1 mol for a Clconcentration of 002-02 mol/l. and particularly when the Q05 concentration is 0.05 mol/l. for a Clconcentration of 0.1 mol/1., the anode element can be made properly porous and the effect of increasing the surface becomes maximized.

(3) The concentration of the inorganic acid added to prevent the precipitation of aluminum hydroxide during the etching, should preferably be higher from the viewpoint of lowering the pH, but it has a certain upper limit since the etching of the anode element to make it porous by the above-mentioned liquid must not be affected. The upper-limit of the amount of nitric acid and sulfuric acid that can be added to a liquid of which the Clconcentration is 0.1 mol/l. and the Crop" concentration is 0.05 mol/l. is 0.2, mol/1., and the upper limit of phosphoric acid is 0.4 mol/l. Also, the upper limit of the amount of nitric acid and sulfuric acid that can be added to a liquid of which the 01- concentration is 0.2 mol/l. is 0.8 mol/l. and the upper limit of phosphoric acid in this case is 0.8 mol/1.

(4) The higher the etching temperature, the greater the surface increase (magnification of etching), but 65-85 C. is the optimum temperature from the practical viewpoint.

(5) Greater eflect can be achieved by using the etching method of this invention in combination with the conventional etching method.

(6) As described above, this invention exhibits a particularly valuable effect in the etching of a thick aluminum plate.

The drawings will now be described in greater detail.

FIG. 1 shows the effect on increase of porosity (magnification) in a 50 v. formation when the temperature of the liquid is varied in the examples of this invention. Curve 1 corresponds to Example 1 and curve 2 corresponds to Example 3.

FIG. 2 shows the effect on magnification in a 50 v. formation when the pulsation factor of the etching voltage is varied according to the examples. Curve 1 corresponds to Example 1 and curve 2 corresponds to Example 3. It can be seen from this figure that 1.5-3 is the optimum pulsation factor.

FIG. 3 shows the variation of magnification in a 50 v. formation when the current density is varied according to the examples. Curve 1 corresponds to Example 1 and curve 2 corresponds to Example 3. It can be seen from the figure that the influence of current density is not great.

FIG. 4 shows the relation between the formation voltage and the magnification of etching. Curve 1 corresponds to Example 1 and curve 2 corresponds to Example 3 with curve 3 corresponding to the conventional etching method.

EXAMPLES Example 1: A smooth aluminum plate of a purity of 99.99% and a thickness of 1 mm. was etched electrolytical- 1y for 10 minutes in an aqueous solution of HCl of 0.1 mol/l. and Q0, of 0.05 mol/1., at C., using a pulsating current of single phase full wave (pulsation factor 1.6) with a current density of 0.6 a./cm. This was formed at 50 v. and then the electrostatic capacity on both surfaces of 1 cm. was 19 ,uf. This is 79 times as great as the case of the smooth surface.

Example 2: An aluminum plate of a thickness of 1 mm. was etched electrolytically for 10 minutes in an aqueous solution containing 0.1 mol/l. of HCl, 0.05 mol/l. of CrO and 0.1 mol/l. of HNO at 80 C., by the use of a pulsating current of single phase full wave of a current density of 0.6 a./cm. The same magnification as in Example 1 was obtained. Furthermore, settlings of aluminum hydroxide were precipitated when a current of 10 a.h.- was flowed per 1 liter of the liquid of Example 1 including no HNO but in the case of the liquid of this example including HNO the settlings of aluminum hydroxide did not precipitate until the current was increased to 35 ab. per liter of the liquid. The increase of the bath voltage was also slight making it possible to continue etching under a stable condition. y

Example 3: A smooth aluminum plate of a purity of 99.99% and of a thickness of 1 mm. was first etched electrolytically, weakly for 60 seconds in an aqueous 16% solution of HCl at 70 C. by a direct current of a current density of 0.7 a./cm. including no ripple and was then etched deeply by the method of Example 2. This was formed at 50 v. The electrostatic capacity on both surfaces of 1 cm. was 21 ,uf. and the magnification of etching (surface increase) as against the smooth surface was 87 times.

Example 4: An aluminum plate was etched electrolytically in an aqueous solution including 0.2 mol/l. H PO instead of HNO in Example 2 and by the same method as the case of Example 2. The same magnification and stability as in Example 2 were obtained.

Example 5: An aluminum plate was etched electrolytically in an aqueous solution including 0.1 mol/l. H 80 instead of HNO in Example 2 and by the same method as the case of Example 2. The same magnification and stability as in Example 2 were obtained.

Example 6: A smooth aluminum plate of a purity of 99.99% and a thickness of 1 mm. was dipped for 90 seconds in an aqueous solution containing 5% H01 and 0.3% CuSO at a bath temperature of 65 C. The copper precipitated on the aluminum plate was resolved (dissolved) and removed by dipping the plate in a cold concentrated nitric acid. The thus etched aluminum plate was then etched deeply by the method of Example 2. The porous aluminum plate thus obtained was formed at 50 v. and then the electrostatic capacity amounted to 90 times that of the smooth surface.

Example 7: An aluminum wire of a purity of 99.99%

and a diameter of 3 mm. was etched electrolytically and was made porous by the same method as Example 4. This was formed at v. and then the electrostatic capacity per 1 cm. of the wire was 8 f. This is times as great as the electrostatic capacity of the wire the surface of which is left smooth.

When a red ink is dropped onto the surfaces of the aluminum anode elements obtained by the methods of the above-mentioned examples, the reverse surfaces turned red. Thus it is shown that the etched holes penetrate through the elements.

We claim:

1. A method of manufacturing aluminum electrolytic condensers, which comprises electrolytically etching the aluminum as the anode using a pulsating current :with a pulsation factor of 1.5-3 in an aqueous solution consisting essentially of 002-02 mol/l. Cl" and 0.020.1 mol/l. CrO in a pH range at which the precipitation of aluminum hydroxides is minimized.

2. The method of claim 1, wherein the etching bath is at a temperature of 6585 C.

3. The method of claim 1, wherein 0.050.4 mol/l. HNO is added to maintain the pH within said range.

4. The method of claim 3, wherein the aqueous solution is at a temperature of 65-85 C.

5. The method of claim 1, wherein 0.050.8 mol/l. H PO is added to maintain the pH within said range.

6. The method of claim 5, wherein the aqueous solution is at a temperature of 6585 C.

7. The method of claim 1, wherein 0.050.4 mol/l. H is added to maintain the pH within said range.

8. The method of claim 7, wherein the aqueous solution is at a temperature of 65-85 C.

References Cited UNITED STATES PATENTS 2,721,835 10/1955 Axtell 204141 2,755,238 7/1956 Turner 204141 2,930,741 3/1960 Burger et al. 204-141 3,035,990 5/1962 Davis et al 2-04-33 3,085,950 4/1963 Thomas et a1 204141 3,249,523 5/1966 Post et al 20414-1 3,321,389 5/1967 Anderson 204-141 ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 

